Applicant has previously proposed a technique for producing a bulky sheet, which involves reinforcing a nonwoven fabric made of entangled fibers with a net-form sheet and heat-shrinking the net-form sheet to form projections and depressions thereon (see Patent Literatures 1 and 2). Besides this type of bulky sheet, Applicant has also proposed another type of bulky sheet that includes a fiber aggregate made by water needling of a fibrous web, wherein the fiber aggregate is formed to have a multitude of projections and depressions (see Patent Literature 3). The projections and depressions in this bulky sheet are formed by rearrangement of the constituent fibers of the fiber aggregate due to the water needling process applied thereto, which renders a zigzag form to the fiber aggregate in its thickness direction.
The sheet produced according to the method of Patent Literature 1 or 2 has an appropriate amount and extent of projections and depressions and is soft and pleasant to the touch. However, since the projections are made by heat-shrinking of fibers, the fiber density in the projections tends to become high. Thus, there still is room for improving the capability of the constituent fibers of the projections to trap dirt such as dust balls.
Meanwhile, the sheet produced according to the method of Patent Literature 3 is capable of trapping and retaining dust among the constituent fibers and is also capable of trapping and retaining relatively-large dirt with its projections and depressions, such as bread crumbs that cannot be trapped among the constituent fibers. However, when high-speed production is applied to this type of sheet to increase productivity, the sheet receives a high tension while being carried, and this may reduce the bulkiness of the projections and depressions.
Besides the above-described techniques for producing bulky sheets, Applicant has also proposed an through-air, hot-air processing technique as a method for restoring the bulkiness of a continuous sheet having been wound into a roll shape and whose bulkiness has thus been reduced (see Patent Literature 4). Patent Literature 4, however, describes nothing about the possibility of applying this hot-air processing technique to the production of sheets having the structure as disclosed in Patent Literatures 1 to 3.